This invention relates in general to rate responsive cardiac pacemakers, and in particular to a pacemaker whose rate response gain factor or slope adjustment is automatically provided in relation to cardiac-related physiological characteristics of a patient.
Rate response gain factor or slope adjustment is an important aspect in cardiac pacemaker operation as physiological consideration of a patient becomes more and more integrated with treatment modes. Further, because of the vagaries among patients, pre-set and solely manually adjustable arbitrary settings in a pacemaker device to regulate pulse delivery rates are not practical or in the best interest of the patient. Individual testing sessions for each patient, while perhaps desirable, are not practical because of time and money investments needed for such a program.
It is, of course, obvious that increased patient activity requires increased pulsed delivery from a pacemaker. However, it is important that this increased pulse velocity have a physiological relationship to its need. Measurements that have cardiac relevance to pulse velocity requirements include minute volume, general patient activity which can be equivocated to accelerometer response in a so equipped pacemaker, right ventricle stroke volume, right ventricular pressure, blood oxygen level, central venous blood temperature, and the like.
It is therefore a primary object of the present invention to provide a cardiac pacemaker which captures peak values of at least one cardiac-related physiological measurement over a consecutive preset number of time segments and then provides for automatic adjustment of the rate response slope.
It is a further object of the present invention to provide a cardiac pacemaker which compares peak values of two separate physiological measurements wherein one such measurement must reach a preset threshold level before peak values of the other measurement are captured over a number of present time segments for use in pulsing rate adjustments.
Another object of the present invention is to provide a cardiac pacemaker which compares minute volume measurements to patient activity measurements and captures peak minute volume levels coincident to significant patient activity levels as exemplified by accelerometer values exceeding a threshold level over a plurality of separate time segments.
It is a further object of the present invention to provide a cardiac pacemaker which captures the minute volume ratios of each peak minute volume measurement and thereafter averages these ratios over the plurality of time segments.
Yet another object of the present invention is to provide a cardiac pacemaker having control signal generating means for adjusting a rate response gain factor of the pacemaker such that peak minute volume ratios achieve a pre-determined heart-rate target value during periods of peak patient activity.
These and other objects of the present invention will become apparent throughout the description which now follows.